This invention relates to a polychloroprene-base adhesive. More particularly, the invention relates to a novel and improved polychloroprene-base adhesive which consists of: (1) resinous material having a softening point of 145.degree.C or higher which is obtained by polymerizing cracked oil fractions of crude petroleum or its distillation products; (2) polychloroprene; (3) known additives for polychloroprene such as metallic oxides and antioxidants; (4) known resins added to polychloroprene-base adhesive such as alkylphenol resin and coumarone-indene resin, if necessary; and (5) volatile organic solvents.
Generally speaking, the polychloroprene-base adhesives have good adhesive strength, and in addition, they have excellent weather resistance, aging resistance, alkali resistance and so forth. Furthermore, they can be applied to a wide variety of substrates to be adhered. So that, the polychloroprene-base adhesives are advantageous in use as compared with several natural rubber-base adhesives, vinyl acetate-base adhesives and methacrylic ester-base adhesives.
For this reason, the polychloroprene-base adhesives are widely employed in the manufacturing industries; however, in the practical use of the adhesives, the retention time of tackiness of the adhesive as used has a very important significance in the adhesion process. That is, when an adhesive having a long retention time of tackiness is used, the open time after the application of adhesive to the bonding step can be extended because, even when the articles are not joined together just after the application of the adhesive, the adhesive strength does not decrease. This fact is very advantageous not only in the convenience during the adhesion process but also in the elimination of the scattering of adhesive strength owing to the changes of open time.
With regard to the retention time of tackiness, the polychloroprene-base adhesives in the prior art have not been satisfactory for the industrial purposes. While, in order to extend this retention time of tackiness, it has been proposed to add thermoplastic resin such as coumarone-indene resin, terpenephenol resin glycol ester of hydrogenated wood rosin and petroleum resins having lower softening points into the polychloroprene-base adhesives, however, such addition is liable to cause the lowering adhesive strength by the decrease of cohesive force.